Ex vivo blood isolation system

ABSTRACT

A system for the sequential and repetitive aspiration and injection of fluid. The system includes a syringe having an internal volume, a piston to vary the internal volume and a chamber divider for separating the internal volume into proximal and distal reservoirs. The chamber divider is moveable along the chamber and is positioned adjacent the distal end of the chamber prior to withdrawal of fluid into the syringe. The proximal reservoir has a maximum displacement volume for receiving fluid. A flow channel provides flow between the proximal and distal reservoirs and a valve disables and enables flow therethrough. A tensile element links the piston and the chamber divider so that after the piston is moved and the proximal reservoir is filled with a first liquid, the chamber divider is pulled away from the distal end of the syringe to enlarge the distal reservoir and draw the blood into the distal reservoir. A conduit is connected with the syringe and is in communication with the patient&#39;s blood vessel and contains the first liquid. The flow channel and the conduit are sized and configured such that after the maximum volume of first liquid has been withdrawn into the proximal reservoir and the blood has been withdrawn into the distal reservoir, the maximum volume of first liquid is substantially free from blood, and subsequent displacement of the maximum volume of first liquid back through the valve is sufficient to displace all the blood from the syringe when the piston is advanced.

This is a division of application Ser. No. 08/196,455, filed Feb. 15,1994 now abandoned.

BACKGROUND AND SUMMARY OF THE INVENTION

Intravenous drugs are commonly administered utilizing injection througha self-sealing port, including y-adapters and prn adapters (also calledsaline wells or heparin wells). These intravenous systems commonlyinclude deadspace which must be flushed free of the injected drug afterthe drug injection so that drug incompatibility will not occur withsequential injections of different drugs. Drugs are commonly injected insolution utilizing a conventional syringe with a needle or blunt cannulaattached to the end for injection through the port. After the injection,however, a second syringe filled with saline must be inserted throughthe port to flush any residual drug solution from the deadspace of thetubing so that residual drug solution does not remain in this deadspaceto prevent the potential for drug incompatibility should another drug beinjected in the future through this same port. The nurse, therefore,draws up the drug with its solution into a first syringe and drawssaline into a second syringe. The nurse commonly injects the drugsolution through the port and into the patient, then injects the salinethrough the port to flush the drug from the deadspace of the system.Because sharp needles have been associated with significant infectionrisk to hospital personnel, it is common to utilize blunt or protectedcannulas to provide safety during such injections. Since, as discussed,two injections are required to assure that the drug does not remainwithin the deadspace, the nurse must commonly utilize two separatesyringes and two separate cannulas, resulting in considerable expense.Furthermore, multiple injections increase the risk of infection to thepatient and, since such ports are commonly connected closely with anindwelling catheter, the greater the number of such injections, thegreater the potential for manipulation of the catheter, which can resultin thrombosis of the vein. In addition, multiple injections result inincrease in exposure of hospital personnel to potentially infectiousliquids from the patient and increase the amount of time spent indelivering drugs to the patient.

Given the aforementioned problems, there has long been a need for asystem which can allow the nurse to inject a drug solution andsubsequently flush the deadspace of the tubing or catheter utilizing thesame syringe, thereby eliminating the need for multiple entries into theport and its associated problems.

An additional problem exists with automatic infusion devices whichutilize syringes. These devices are commonly used for injection ofmedication into patients and do not require close attention by hospitalpersonnel. However, once the infusion of these devices is complete, thedrug may remain within the patient's vein and the deadspace of thetubing if the hospital personnel do not promptly arrive to flush thedrug from these areas with saline solution. This can result in potentialinjury to the patient's vein, thrombosis, precipitation of the drugwithin the tubing, or chemical incompatibility and precipitation ifanother nurse fails to recognize the presence of drug within the tubingand injects a different incompatible drug into the tubing system. Thereis, therefore, a need for a system which can automatically flush thetubing after an injection whether or not the injection is provided bythe nurse or a mechanical or electronic infusion device. This wouldallow more safe unattended injection by mechanical devices in the homesetting. U.S. Pat. No. 4,857,056 describes a system for providingautomatic infusion of a drug followed by a flush solution. This device,however, requires the provision of two syringes and many mechanical andelectronic infusion devices are designed to interface with a singlesyringe. Furthermore, two syringes result in additional expense whencompared with a single syringe system.

As hospital costs increase, it has become desirable to reuse disposablemedical equipment for the same patient for short periods of time (forexample, 24-96 hours). It is, therefore, advantageous to provide amultiple use syringe for use with a single patient over multipleaspirations and injections of sequential medications. U.S. Pat. No.4,439,184 discloses a single syringe for the injection of two differentdrugs. The syringe has proximal and distal chambers and two pistons anda proximal no-pass region and a distal by-pass region. However, thissyringe can only provide a single sequential injection from eachcompartment since there is no provision for withdrawing the distalpiston from the by-pass region for sequential fluid withdrawal or forpresetting the volume of the proximal chamber during the withdrawalmaneuver. Therefore, there is no provision for allowing the nurse toeasily aspirate the respective solutions into the syringe. There arenumerous additional multi-chambered syringes in the prior art: U.S. Pat.No. 5,102,388 discusses a multi-chamber syringe for sequential injectionof different drug solutions. Piercing devices are disclosed whichsequentially pierce stoppers during the injection; U.S. Pat. No.5,125,892 discloses a multi-chambered syringe having a hollowed dilatedpiston which can burst; U.S. Pat. No. 4,655,747 discloses adual-chambered syringe having an inner and outer barrel; U.S. Pat. No.4,610,666 discloses a tandem barrel syringe; U.S. Pat. No. 4,496,344discloses a multiple compartment syringe having a distal bypass region;U.S. Pat. No. 4,464,174 discloses a two-compartment mixing syringe withan inner and outer barrel; U.S. Pat. No. 4,453,934 discloses a pistonhaving a distal container which can fracture for the sequential deliveryof, for example, a contrast agent followed by a saline flush solution;U.S. Pat. No. 3,985,122 discloses a syringe having two bores and twopistons having different diameters for mixing solutions within thesyringe; U.S. Pat. No. 3,807,199 discloses a method for assembling amultiple compartment syringe and for preloading the syringe with ameasured quantity of liquid; U.S. Pat. No. 3,494,359 discloses atwo-compartment syringe utilizing a compartment separator which candeflect for mixing of the solution; U.S. Pat. No. 3,511,239 discloses atwo-compartment syringe having two pistons and a rod extending throughthe pistons with a longitudinal bore which provides communicationbetween the two chambers, allowing the fluid in the upper chamber to bemixed with the drug in the lower chamber; U.S. Pat. No. 4,792,329describes a mixing syringe having a bypass region and three separatestoppers for mixing and subsequently injecting two solutions; U.S. Pat.No. 4,693,706 describes a mixing syringe having inner and outercylindrical barrels for mixing two solutions; U.S. Pat. No. 4,834,714describes a double barrel arrangement capable of achieving the doublecapacity of a single syringe; U.S. Pat. No. 3,680,558 discloses amultiple compartment syringe having telescoping barrels with anintermediate valve which can be opened by rotation; PCT ApplicationWO92/01485 discloses a syringe having a barrel with a cylindrical insertfor long-term storage and subsequent mixing and injection of two drugs.In addition to the foregoing discussion, the above patents provideadditional general background of this invention. Importantly,multi-barrel syringes are associated with additional expense andcomplexity whether in tandem or telescopic configuration. Also, it isexpensive to preload a multi-compartment syringe with flush solution andpre-loading may require the addition of glass or other containers tomaintain stability of the solution, which adds additional expense. Toachieve reduction in cost, it would be advantageous for the nurse toaspirate a specific preset quantity of flush solution into the syringeimmediately prior to use. It would further be advantageous for thevolume of this flush solution to be preset by an indicator so that thenurse is confident that adequate flush volume is present to completelyflush the deadspace of the syringe and the deadspace of conventionalwells when it has been indicated by the indicating means that thesyringe contains adequate flush volume. The present invention functionsto achieve these and other advantages, as will become evident from thefollowing discussion and claims.

Another common problem relates to blood sampling. Syringes have beencommonly used to draw blood out of intravenous lines or arterial lines.However, such blood is commonly diluted with the saline or heparinsolution which generally dwells within the deadspace of the intravenousor arterial line. Problems related to blood collection are described inU.S. Pat. No. 3,835,835, which discloses a multi-barrel two-compartmentsyringe for collecting a pure uncontaminated blood specimen. Anothersystem for isolating pure blood is discussed in my U.S. Pat. No.4,838,855 (the disclosure of which is hereby incorporated by referenceas if completely disclosed herein). This patent describes a system andmethod for repetitively achieving an undiluted specimen of blood outsidea patient for testing or sampling. The system utilizes a variable volumereservoir and predetermined volumes to separate the fluid which isindwelling within the tubing system from the blood and fluid mixturethat naturally occurs upon withdrawal of blood into the tubing. Thisallows the stored fluid within the syringe which is not contaminatedwith blood to be utilized to flush blood from the system after bloodtesting or sampling. This system has the important advantage ofproviding for the separation and isolation of a portion of the originalfluid stored within the deadspace of the tubing from the blood that iswithdrawn into the system so that the isolated fluid can later be usedto flush the blood from the tubing, thereby providing ease of operationand reducing the risk of accumulation of blood within the deadspace ofthe reservoir. The system also minimizes the amount of total fluid addedto the system and the patient during repetitive sampling or testing.

Commonly, however, it is necessary to draw blood at substantialdistances from the indwelling catheter, such as during anesthesia whenthe anesthesiologist is sitting at the head of the bed above the head ofthe patient and wherein the patient is draped by sterile drapes forsurgery. A radial artery catheter is positioned in an arm, which oftenis directed downward at the side of the patient. Therefore, theanesthesiologist is required to sample blood at the head of the bed froman arm positioned near the patient's hip so that the distance may besubstantially greater than 1 meter. In such situations, it wouldadvantageous to store the blood and fluid mixture within a syringereservoir, rather than solely within the tubing itself, since the lengthof the tubing is so great between the patient and the sampling site thata large volume of blood must be drawn into the system to adequatelyclear the line at the sampling site. Furthermore, it is commonlynecessary to draw blood from indwelling catheters that do not have fixedreservoirs attached, such as multilumen catheters. Such catheterscommonly do not conventionally have adequate tubing length to providethe capacitance storage function described in my aforementioned patent.

In addition to these problems, it would be advantageous not to leavecertain toxic drugs or radioactive materials within the deadspace of asyringe or cannula or heparin well after an injection. This isparticularly true with the injection of chemotherapeutic drugs which maybe highly toxic to the nurse providing the injection if the nurse isexposed to even minute quantities of the drug over a sustained period oftime. An injection of a chemotherapeutic agent through a cannula andthen the withdrawal of that cannula can result in minute quantities ofthe chemotherapeutic agent being expelled in the region around theinjection sight or in the environment prior to dropping the cannulaand/or syringe within the waste receptacle. This is also true ofradioactive materials which are commonly injected (for example, duringan exercise stress test) at a time wherein minute quantities are bestcompletely injected into the patient so that there is less potentialexposure of hospital personnel to residual radioactive material outsidethe patient within the deadspace of the cannula or syringe. Although thevolume is small, leaving drugs or radioactive material in the deadspaceis also wasteful when considered collectively throughout the year in alarge hospital.

The present invention functions to specifically, allow the aspiration ofa capacitance storage volume of a flush volume, which can later be usedto flush the deadspace of the reservoir and the deadspace of a tubingsystem and catheter. This invention is usable in many medicalenvironments, including the administration of drugs wherein deadspacedrug must be flushed from the system and the collection of blood whereinthe flush solution must be isolated from undiluted blood to provide apure blood sample or where the deadspace of the syringe must be flushedfree of blood for repetitive fixed reuse with indwelling catheters.

The sequential aspiration syringe comprises a variable volume chamber,such as a syringe barrel or cylinder having an opening which can includea conduit adjacent the distal end for flowing liquid into and out of thechamber. The injection system further includes a volume adjuster, suchas a piston with a handle for adjusting the volume within the variablevolume chamber. The syringe further includes a chamber divider, whichcan be a second piston that is positioned within the chamber. The volumeadjuster is linked to the divider by a connector or tensile element suchas a tether. The tensile element is preferably flexible and collapsible,and preferably filamentous. The chamber divider effectively divides thechamber into two variable volume reservoirs, a proximal or upper primaryreservoir and a distal or lower secondary reservoir. The syringe furtherincludes a flow channel which may be in a fixed position along thebarrel adjacent the distal end or which may be moveable and carried bythe divider piston, or which may be dynamically formed by apositionally-derived flow space or separation between the divider pistonand at least a portion of barrel wall when the divider piston ispositioned adjacent the distal end. The syringe further includes a valvewhich enables fluid to pass through the flow channel around or throughthe chamber divider to pass between the secondary reservoir and theprimary reservoir. The valve can be the divider piston or can be locatedwithin or otherwise carried by the divider piston. The flow channelpreferably provides for bi-directional flow between reservoirs. In onepreferred embodiment, the passage of fluid through the flow channel canbe enabled or disabled by positioning the chamber divider at differentpositions along the chamber. In one preferred embodiment, flow throughthe flow channel is disabled by traction on the tensile element and flowis enabled by contact between the divider and the distal end of thebarrel. The positionally selective enablement and disablement of theventing of fluid about the chamber divider provides a mechanism for thepreset selective adjustment of maximum volume of aspirated fluid withineither the secondary reservoir or the primary reservoir, and for thesequential administration of this fluid from the secondary reservoir andthe primary reservoir. In the preferred embodiment, the primaryreservoir has a fixed maximum volume. The primary and primary reservoirsare in fluid connection with the conduit connected to the distal end ofthe chamber so that fluid may flow from either reservoir through theconduit and out of the injection system.

The stop for stopping the divider piston face from pressing against thetapered end and thereby trapping fluid between the face and the taperedend can be positioned upon the face of the divider piston, along thebore, or can comprise complimentary detents for engaging the handle orthe main piston and thereby preventing further advancing force of thehandle and main piston against the divider piston.

The main piston can reduce pressure within the upper primary reservoir,and the tensile element can selectively lower the pressure in thesecondary reservoir when the tensile element is extended and the primaryreservoir has been filled. The tensile element can provide forequivalent retraction of the main piston and the divider piston when theprimary reservoir has been filled to prevent lowering pressure withinthe primary reservoir even with further retraction on the main piston sothat substantial fluid flow into the primary reservoir would beinhibited even without a valve which disables flow between thereservoirs after primary reservoir filling.

In operation, prior to use, both reservoirs are preferably empty.Initially, there is fluid communication between the secondary reservoirand the primary reservoir. The divider is preferably positioned so thatthe secondary reservoir has very little or no internal volume. Inoperation, the distal conduit is connected to a source of fluid such asa blood line or the distal conduit is connected to a cannula which isinserted into a saline flush vial or the like. The volume of the primaryreservoir is then increased by the volume adjuster to cause flow offluid into the distal conduit and then through the flow channel and intothe primary reservoir. The flow through the flow channel is preferablyenable by positioning the divider adjacent the distal end, which is theresting position of the divider prior to use. During this time, thedivider is preferably restrained from moving, as by a detent, therebypreventing enlargement of the secondary reservoir and assuring thedivider remains in the venting position despite the relative negativepressure within the primary reservoir. This also allows the nurse tofreely turn the syringe upward to expel any aspirated air withouteffecting the contents of the secondary reservoir. When the primaryreservoir is filled (usually with saline), the tensile elementconnecting the volume adjuster and the chamber divider becomes fullyextended and pulls the chamber divider against the restraining detent.This provides tactile indication of completed filling of the primaryreservoir, although other indicating means would also be effective. Thenurse then can connect to a distal conduit to a second liquid sourcesuch as a drug vial. Further retraction then causes the divider todisplace from the venting position. The tensile element is preferablystrong, but of minimum fluid displacement volume, such as a nylonfilament. Upon displacement, the flow channel is closed so thatadditional fluid does not pass into the primary reservoir. The volume ofthe secondary reservoir is then enlarged so that fluid passes throughthe distal conduit into the secondary reservoir until the secondaryreservoir is adequately filled. Again, the nurse can turn the syringeupward after aspiration and expel any aspirated air from the secondaryreservoir without effecting the contents of the primary reservoir. Atthis time, the flow channel which previously provided fluidcommunication between the primary reservoir and the distal conduit isclosed so that fluid cannot flow from the distal conduit into theprimary reservoir. Furthermore, the secondary reservoir is isolated fromthe primary reservoir so that mixing of the fluids between thereservoirs cannot occur. Once both reservoirs have been adequatelyfilled the container now includes two sequentially stored volumes offluid which are isolated one from another and which may containdistinctly different solutions. When injection is desired, each volumeof fluid can now be forced in a sequential fashion back through thedistal conduit in the reverse order in which they were stored. To injectthe fluid, the volume adjuster is advanced, thereby increasing thepressure within the primary reservoir which is transmitted to thesecondary reservoir. When the pressure within the secondary reservoir isincreased, fluid can move from the secondary reservoir into the distalconduit. However, during this time, the flow connection between thedistal conduit and the primary reservoir is disabled so that flow cannotmove from the primary reservoir to the distal conduit even if pressureis increased within the primary reservoir. With advancement of thevolume adjuster, the primary reservoir moves along the chamber whilemaintaining a constant volume, the hydraulic force of the trapped liquidcausing the divider to advance. Once the secondary reservoir hasemptied, the flow between the primary reservoir and the distal conduitis enabled. The enablement is preferably induced when the divider entersthe venting region adjacent the distal end of the chamber and may beactivated by contact with the distal end of the chamber. Means toindicate enablement of vented flow can be included such as a markerlocated at a position of the handle or a detent. When the divider is inthis position, flow can occur between the primary reservoir and thedistal conduit. During this time, as the primary reservoir empties, thetensile element collapses, coils, or folds such that the movement of thevolume adjuster toward the divider is preferably not inhibited. In thisway, it can be seen that at least two different fluids may besequentially withdrawn into and stored within the chamber and isolatedone from the other by first withdrawing fluid in the primary reservoirand then withdrawing a different fluid into the secondary reservoir.These fluids may then be injected sequentially in the reverse order ofaspiration, first from the secondary reservoir and then from the primaryreservoir. The fluid from the primary reservoir is preferablycircumferentially expelled through the deadspace of the secondaryreservoir and conduit to allow a complete flush of the system and thevolume of the primary reservoir can be preset to assure a complete flushof the secondary reservoir and conduit. Also, this sequential aspirationand injection preferably occurs through the same distal conduit so thatthere is no need to disconnect and reconnect for sequential aspirationand/or injection of fluids. It can be seen that when the flow channel isnot in fluid connection with the primary reservoir that the primaryreservoir and the two pistons represent a single retractable pistonassembly with a proximal and distal portion separated by the primaryreservoir and with a fixed internal volume and with a fixed pistonassembly length, as defined by the tether element. The piston assemblycan move along the barrel and the piston assembly can collapse toshorten in length when the fluid escapes from the primary reservoir andcan enlarge in length when fluid enters the primary reservoir, bothshortening and lengthening occurring to movement of the proximal portiontoward or away from the distal portion.

An example of use is with blood sampling, wherein fluid without bloodadmixture can be stored in the primary reservoir and blood and fluidmixture can be stored in the secondary reservoir. Alternatively, for theadministration of drug solutions, it can be seen that saline can beinitially drawn into the primary reservoir and the drug solution drawninto the secondary reservoir. When the distal end of the distal conduitis then connected to an intravenous line of a patient, the reservoirsare emptied in the reverse order in which they were filled such that thedrug solution is injected into the patient followed by the injection ofsaline. All of this can be achieved with much greater simplicity sincedisconnection and reconnection of multiple syringes are no longernecessary when utilizing this device.

In another system embodiment for blood sampling, the syringe can bepermanently attached a second conduit which is connected to a firstconduit with an access port intermediate the first and second conduit.The first conduit is connected to a terminal of a conventional catheter,for example, a multilumen catheter. (These catheters often have a lowinternal fluid volume so that very little resident flush solution isavailable within the catheter for filling the primary reservoir.) Thefirst conduit of the system includes an access port which can beutilized for drawing a blood specimen or for infusing liquid. Indeed, anintravenous tubing could be connected to this access port so that liquidcan continuously infuse through this port when a blood sample is notbeing obtained. The maximum displacement volume of the primary reservoircan be preset so that it is less than the internal fluid volume of thefirst conduit, the second conduit, and the internal fluid volume of thecatheter. In this way, this volume can be preset so that, uponwithdrawal of fluid into the syringe, only flush solution will enter theprimary reservoir. The syringe can, therefore, can be used to draw freshpure blood past the access port for sampling by insertion of a cannulathrough the access port. It is considered preferable to have a minimaldeadspace intermediate the syringe and the access port so as to provideadequate saline flush of all residual blood from the deadspace withminimal flush volume. The system can be constructed such thatsubstantial priming deadspace of resident flush solution is suppliedwith the first conduit intermediate the access port and the bloodvessel. This assures that adequate flush volume is present so that theprimary reservoir can aspirate a large enough flush volume to laterprovide an adequate flush of the primary conduit and the deadspaceintermediate the syringe and the access port. In another embodiment, theaccess port is positioned adjacent the distal end of the syringe so thatsubstantially no deadspace is present between the distal end of thesyringe and the access port, thereby further minimizing the requirementfor higher flush volumes. Whether the access port is placed withoutdeadspace in juxtaposition with the syringe or whether the access portis connected by a low deadspace conduit will depend upon whether it isdesirable to place the syringe directly upon the catheter or at somedistance from it. In any case, the volume of the secondary conduit ispreset during manufacture to be less than the internal fluid volume ofthe catheter and the conduit portions distal the syringe. Subsequenteach blood aspiration maneuver, some blood mixed with fluid will remainwithin the first conduit or catheter and this can be easily flushed byinserting a cannula into the access means and flushing saline throughthe access means. Also, with this system, any source of fluid which isconnected to the second conduit or otherwise proximal the access meanscould effectively flush any residual blood distal the access means aftereach blood withdrawal maneuver.

It is, therefore, the purpose of this invention to provide an apparatusand method that will eliminate the need for multiple syringes for theadministration of drugs through IV systems. It is further the purpose ofthis invention to provide a simplified method and apparatus for thesampling of blood from an indwelling catheter within a patient's bloodvessel which does not require the use of a first syringe to withdraw anddiscard the resident portion of fluid within the catheter and associatedtubing system. It is further the purpose of this invention to provide asystem for withdrawing blood into a syringe and flushing the blood backout of a syringe utilizing reciprocating saline volumes with minimaladditional volume administration to the patient and further simplifyingthe process of syringe flushing, as for repetitive undiluted bloodisolation within arterial lines for sampling or ex vivo testing. It isfurther the purpose of this invention to provide an inexpensive devicewhich allows blood collection and drug administration with a singleunified apparatus, thereby reducing overall cost of manufacture. It isfurther the purpose of this invention to provide an inexpensive bloodcollection and drug administration system which utilizes a novel, simplemethod of sequential withdrawal of liquid followed by sequentialinjection in the reverse order of the withdrawal, which method simulatesconventional single syringe aspiration and injection, thereby providinggreater ease of use for nursing personnel. It is further the purpose ofthis invention to provide an apparatus having an inexpensive means, suchas a filamentous tensile element, for adjusting the maximum volumewithin the primary reservoir during manufacture so that a wide range ofsuch devices having different maximum volumes can be manufactured fordifferent applications without substantial increase in manufacturingcost. It is further the purpose of this invention to provide a singleunified apparatus and method for the compartmentalization and isolationof two different fluids within a single syringe utilizing a singlewithdrawal maneuver and to allow the nurse to expel aspirated air fromeither compartment during each withdrawal process and to provide thesubsequent sequential injection of these two different fluids utilizinga single injection maneuver. It is further the purpose of this inventionto provide a multiple reservoir syringe which includes a bi-directional,positionally-enabled, circumferentially-directed flushing and aspiratingmechanism which freely vents a high flow of fluid from a primaryreservoir upon completed injection of liquid from a secondary reservoirto completely flush the secondary reservoir free of blood or drugsolution with a minimum volume of fluid. It is further the purpose ofthis invention to provide and inexpensive system for connecting, withina syringe sequential pistons with a tensile element of low fluiddisplacement volume and high flexibility to allow delayed distal pistonretraction at a predetermined volume during proximal piston withdrawaland subsequent uninhibited proximal piston advancement toward the distalpiston to achieve a simplified method of sequential aspiration andflushing and so that the internal volume of the syringe is notsignificantly effected by the displacement volume of the element. It isfurther the purpose of the invention to provide a mechanism fordisabling flow between a proximal and a distal reservoir which isactivated at a specific filling volume of the primary reservoir andwhich is activated by retraction of a tensile element. It is further thepurpose of this invention to provide an automatic flushing syringe whichcan be used with automatic, electronic, or mechanical injection systemsfor unattended injection and subsequent flush into a patient with asingle syringe. These and other objects and advantages of the inventionwill be further set forth in the description which follows and, in part,will be learned from the description or may be learned by practice ofthe invention. The objects and advantages of the invention may berealized by means of the instrumentalities and combinations particularlypointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic elevational view partly in cross-section of asequential compartmentalized fluid aspiration and injection syringe inaccordance with the present invention;

FIG. 2 is a view similar to FIG. 1 showing the piston in the retractedposition;

FIG. 3 is a schematic cross-sectional view taken along line 3--3 of FIG.2;

FIG. 4 is a detail of area 4 in FIG. 2;

FIG. 5 is a detail of area 5 in FIG. 1;

FIG. 6a is a schematic illustration of a syringe in accordance with thepresent invention in operation for blood sampling;

FIG. 6b is a view similar to FIG. 6a showing the syringe plunger beingretracted;

FIG. 6c shows the filled syringe allowing for blood transfer to acontainer;

FIG. 7 show the syringe of the invention following blood transfer to thecontainer;

FIG. 8 is a schematic illustration of a syringe in accordance with theinvention incorporated into a blood aspiration assembly;

FIG. 8a is an enlargement of an area of FIG. 8;

FIG. 9 shows the blood aspiration assembly of FIG. 8 in blood samplingmode;

FIG. 9a is an enlargement of an area of FIG. 9;

FIG. 10 is an enlarged elevational view of a syringe in accordance withthe invention for use in drug solution administration;

FIG. 11 is a view similar to FIG. 10 showing the syringe plunger beingretracted;

FIG. 12 shows the partially filled syringe being aligned with a drugvial;

FIG. 13 is a view similar to FIG. 12 showing the plunger furtherretracted to load a drug;

FIG. 14 is a schematic illustration of a syringe in accordance with theinvention incorporated into a blood aspiration assembly;

FIG. 15 is an elevational view of a presently preferred embodiment forutilizing conventional syringe barrels and in which the piston is beingretracted to load saline;

FIG. 16 is a view similar to FIG. 15 showing further retraction of thepiston to load a drug;

FIG. 17 is a view of the syringe of FIG. 16 in which the piston is beingadvanced to administer the drug to a patient;

FIG. 18 is a view similar to FIG. 17 showing the administration ofsaline following administration of the drug;

FIG. 19 is an enlarged view of the piston structure shown in FIG. 18;

FIG. 19a is an enlargement of area 19a of FIG. 19;

FIG. 20 is a view taken along line 20--20 of FIG. 19;

FIG. 21 is a view taken in the direction of line 21--21 showing fluidflow in the syringe of FIG. 19;

FIG. 22 is an enlargement of the tether structure of FIGS. 15-21;

FIG. 23 shows a syringe in accordance with the invention incorporated inan automatic syringe pump.

DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The sequential compartmentalized fluid aspiration and injection syringe5 (FIG. 1) includes a syringe barrel 10 having a proximal base 12 and adistal tapered portion 14 extending to distal tip 18. The syringe barrelincludes a main bore 22 which is in fluid connection with distal conduit26 extending through the distal tip 18. The apparatus includes a mainpiston 38 having a handle 34 including inner face 39 and wipers 40 and42. Piston 38 is preferably comprised of lubricated rubber. Theinnerface 39 includes a recess 44 with a retaining lip 46. The handle 34includes distal tip portion 50 which can be forced through the recess 54in the piston 38. After insertion through the recess 54, the handle tip50 is retained within the piston 38. The apparatus further includes ancylinder divider piston 58 which preferably appears relatively similarto the main piston 38 and can be similarly fashioned. Divider piston 58is likewise preferably comprised of lubricated rubber having lateralsealing portions as distal wiper 60 and as proximal wiper 62. Thedivider piston 58 has a lower face 59 that is preferably sloped toconform with the tapered distal end 14. The divider piston 58 furtherincludes an upper face 72 with a recess 76 having lip 78 for receiving atether retainer 80, as will be described. A connecting tensile elementor tether 84 is provided, which is preferably filamentous and of lowfluid displacement volume, having a proximal tether retainer 82 and adistal tether retainer 80 for respective insertion and retention withinthe piston 38 and the cylinder divider piston 58, respectively. Thetether 84 is preferably comprised of a flexible material such aspolyethylene or nylon filament and may be integral with or otherwiseattached to the tether retainers 80 and 82. The tether 84 preferablyshould have substantial tensile strength and preferably should be ableto withstand a 10-15 pound longitudinal pull force without breaking. Thediameter and shape of the bore 22 of the syringe barrel 10 and thediameter and shape of the piston 38 and cylinder divider piston 58 areall matched so that the piston 38 and the cylinder divider piston 58seal tightly within the main bore 22 of the syringe barrel 10. The bore22 diameter is uniform along the main portion 85 of the barrel 10 toprovide uniform seating and sealing of the main piston 38 and cylinderdivider piston 58. A vent portion 100 is provided adjacent the taperedportion 14 of the syringe barrel 10. In the preferred embodiment, thevent portion 100 includes multiple flow channel slots 104 having anaxial length which is greater than the length of the cylinder dividerpiston 58. The slots 104 are separated by radially projecting linearribs 106, each having a smooth innersurface 108. The diameter of thesyringe bore 22 when measured transversely from the innersurfaces 108 ofopposing ribs is equivalent to the diameter of the syringe bore 22throughout the length of the barrel main portion 85 so that the cylinderdivider piston 58 is seated against the innersurfaces 108 of radiallyprojecting ribs 106 when the cylinder divider piston 58 is positionedwithin the venting portion 100, as shown in FIG. 1 and FIG. 11. Thisallows free reciprocating movement over the slots 106 with maintenanceof stability of the divider piston 58. Several seats 109 are providedwhich prevent contact of the lower face 59 against the taper portion 14,thereby forming, upon complete advancement of the divider 58, acircumferential flush flow space 116. The seats or stops 109 preferablyinhibit advancement of the lower face 59 beyond a distance of 2 mm fromthe tapered portion; although, up to 5 mm is acceptable when largerflush volumes are being used. The small size of the flush space 116allows complete flushing with minimum flush volume. Several of the ribs106 can include radially projecting detents 118 to retain the cylinderdivider piston 58 in the venting position by engaging the distal wiper60, as shown in FIG. 5. Other means for retention may be used. Forexample, the transverse diameter of the syringe bore 22 may be slightlyreduced (not shown) at the level of the ribs 106 so as to provide slightcompression of the cylinder divider piston 58 to reversibly retain thecylinder divider piston 58 within the vent portion 100.

In assembly, the tether retainers 80 and 82 are inserted into theirrespective recesses 76 and 44 of the cylinder divider piston 58 andpiston 38. The reservoir divider piston 58 and the piston 38, with itsattached handle 34, are inserted into the syringe barrel 10. When soassembled, syringe 5 defines a chamber 64 (FIG. 2) which is divided bythe cylinder divider piston 58 into two separate variable volumereservoirs, a primary reservoir 66 and a secondary reservoir 68. Thehandle 34 is then fully advanced so that the innerface 39 of piston 38forces the cylinder divider piston 58 into the venting position adjacentvent portion 100 past detent 118 against the seats 109 with the cylinderdivider piston 58 (as in FIG. 1) contacting the ribs 106 and the piston38 being adjacent the cylinder divider piston 58 and the circumferentialflow space 116 between face 68 and tapered portion 14, (as is shown inFIG. 1 and FIG. 5).

The method of operation depends upon the environment in which theinvention is being used. One of the primary advantages of the presentinvention is the fact that this syringe can be utilized for severaldifferent operations which previously involved either the use ofsequential aspiration utilizing two separate syringes (as duringintermittent blood sampling) or sequential injection utilizing twoseparate syringes (as in IV drug administration) or both sequentialaspiration and sequential injection (as in repetitive blood isolationfor testing or sampling from arterial lines.) The utilization of asingle apparatus which can accomplish many widely-used tasks within thehospital provides additional value in that familiarity with the deviceis increased and the cost can be reduced by increased utilizationthroughout many different hospital areas.

In operation for blood sampling, the syringe 5 can be used in severaldifferent ways. For example, when repetitive blood sampling is notrequired, the nurse can utilize the device as a single disposable unitto collect and transfer a single blood specimen. This transfer operationis illustrated in FIGS. 6 and 7. A needle or cannula 111 is attached tothe distal tip 18. A protected needle or cannula, such as described inmy U.S. patent application Ser. No. 08/043,636 (the disclosure of whichis hereby incorporated by reference as if completely disclosed herein)may be used. The cannula 111 is inserted through the septum 118 of aterminal 113 of a catheter 114 within the blood vessel 115 of a patient.The handle 34 is retracted and the initial fluid contained within theterminal 113 and the catheter 114 is drawn into the distal conduit 26 ofthe syringe 5 and flows through the flow channel slots 104 of the ventportion 100 around the cylinder divider piston 58 into the secondaryreservoir 68. The primary reservoir 66 is filled until the tether 84becomes fully extended. During this time, the divider is retained bydetents 118 so that the secondary reservoir 68 does not enlarge. Inaddition, since the tether 84 is not extended, there is no pull againstthe divider piston 58. The slots 104 and circumferential flow space 116preferably have cross-sectional areas at least equal to that of thedistal conduit 26 so that fluid can rapidly flow around the dividerpiston 58 to reduce the potential for a relative vacuum to develop inthe secondary reservoir 68 which could displace the divider 58 out ofthe venting position. Once the tether 84 is fully extended, the primaryreservoir 66 is filled. At this time, further retraction upon thesyringe handle 34 causes the extended tether 84 to retract dividerpiston 58 out of the venting position, overcoming detent 118 andresulting in displacement of the cylinder divider piston 58 proximally,as in FIG. 2. Generally, a slight increase in force is required todisplace the cylinder divider piston 58 from the fully advanced positionby overcoming the detents 118. This slight increase in resistanceprovides a useful indication for the nurse that the syringe 5 is nowwithdrawing pure blood into the secondary reservoir 68, as will bediscussed. A mark 130 (FIG. 7) can also be provided on the handle 34 forthis purpose. As noted, continued withdrawal of the handle 34 after thetether 84 has reached its maximum length will cause the tether 84 topull the cylinder divider piston 58 from its vented position and thiswill bring the proximal wiper 62 into complete sealing contact with thesmooth circumferentially continuous bore 22 of the barrel 10.Immediately upon movement of the cylinder divider piston 58 to the end120 of the vent portion 100, the slots 104 of vent portion 100 arethereby sealed closed to the primary reservoir 66 by the proximal wiper62 so that no further fluid may move through the slot 104 into theprimary reservoir 66. The primary reservoir 66 is therefore completelyisolated from the secondary reservoir 68 by the tight seal provided bythe wiper 62 and wiper 60 against the smooth continuous bore 22. Thisfixes the volume within the primary reservoir 66 and this volume istherefore a function of the length of the fully extended tether 84 andthe diameter of the bore 22. Further withdrawal of the handle 34 willcause the piston 38 to cause further retraction upon the cylinderdivider piston 58, thereby pulling the cylinder divider piston 58further proximally and drawing pure blood into the secondary reservoir68. Actually, once the wiper 62 has established a completecircumferential seal, the tether is no longer necessary for retractionsince the divider 58 will retract with the piston 38 to accommodate thenegative pressure produced by withdraw of the piston 38. The tether 84,therefore, functions as a valve activator and volume adjuster by settingthe volume of the primary reservoir 66 at which volume the primaryreservoir 66 will be filled and sealed. A pure undiluted blood sample isassured by setting the length of the tether 84 in assembly to provide anadequate volume to remove all resident fluid from the catheter 114 andterminal 113. Generally, a primary reservoir 66 volume of 5 cc isadequate to assure that all resident fluid has been removed from mostconventional catheters and terminals, such as multilumen central venouscatheters. Once the pure blood sample has been withdrawn into thesecondary reservoir 68, the cannula 111 can be removed from the terminalof the multilumen catheter and then inserted into, for example, anevacuated container 140, as shown in FIG. 6c. A blood transfer apparatussuch as that shown in my U.S. Pat. No. 5,114,400 (the disclosure ofwhich is hereby incorporated by reference as if completely disclosedherein) may be used and, at this point, pure blood can be transferredfrom the secondary reservoir 68 into the evacuated container 140.

In this way, it can be seen that the syringe 5 accomplishes automaticseparation of the "discard volume" of resident fluid (which will bemixed with some blood) in the primary reservoir 66 from the undilutedblood sample in the secondary reservoir 68. A volume of 5 cc of theprimary reservoir is generally suitable to provide an adequate "discardvolume" when the device is used for most conventional central venouscatheters. The separated pure blood sample within the secondaryreservoir 68 can then easily then be transferred into an evacuatedcontainer for transport to the laboratory.

The sequential compartmentalized fluid withdrawal and injection syringe5 can also be incorporated into a blood aspiration assembly, asdisclosed in my U.S. Pat. No. 4,838,855 (the disclosure of which ishereby incorporated by reference as if completely disclosed herein). Theblood aspiration system 200, shown generally in FIGS. 8-9, includes afirst conduit 204 which is connectable to a catheter 208 for insertioninto a blood vessel 209. The first conduit 204 engages an ex vivomeasurement apparatus sensing unit for measurement of the partialpressure of oxygen, carbon dioxide, and other parameters, as are knownin the art. Additionally provided along the first conduit 204 is a bloodaspirator receiver 210 which can include a resealable septum 211 whichcan be of the type as described in my U.S. Pat. No. 5,178,607 (thedisclosure of which is hereby is incorporated by reference as ifcompletely disclosed herein). The system further includes a secondconduit 212 which is connected to a valve 214, such as a conventionalstop-cock. A third conduit 218 can be provided which is connected to ahigh pressure fluid source (for example, a bag of pressurized salinesolution). In addition, a pressure transducer may be provided and ispreferably positioned along the third conduit 218. A one-way flush valve230, as is known in the art, is further provided intermediate the highpressure source and a syringe 5'. The syringe 5' is of the design asdiscussed supra and is provided with barrel 10' and bore 22' andincluding the piston handle 34' and piston 38' which is connected by atether 84' (FIG. 9a) to a cylinder divider piston 58', defining aprimary reservoir 66' and a secondary reservoir 68'.

In operation, the system 200 is normally filled with resident fluid,such as heparin solution or saline, and connected to catheter 208 whichhas been inserted into the blood vessel 209 of a patient. During thistime, the valve 214 is closed to the syringe 5' and opened to providefluid communication between the high pressure source and the bloodvessel 209. Furthermore, during this time, the pressure within the bloodvessel 209 can be monitored by the pressure transducer. When a bloodsample is desired, the valve 214 is positioned so that fluidcommunication is opened between the syringe 5' and the blood vessel 209and closed to the high pressure source. At this time, both the piston38' and the cylinder divider piston 58' are in the fully advancedposition and the cylinder divider piston 58' is in the vented positionagainst the ribs 106' (as shown in FIG. 8a). When a blood sample isrequired, the nurse withdraws the handle 34' which retracts the piston38', withdrawing the resident heparin solution from the second conduit212 through the slots 104' and into the primary reservoir 66'. Themaximum volume of the primary reservoir 66' is set by the length of thetether 84 and predetermined to be less than the combined internal fluidvolume of the first and second conduits 204 and 212 so that no blood, ornegligible amounts of blood, enters the primary reservoir 66' and sothat the primary reservoir 66' is completely filled with the residentflush solution. The operation, advantages, and rationale for this novelreciprocating volume relationship is discussed in detail in my U.S. Pat.No. 4,838,855 and further in the medical journals, Critical CareMedicine, vol. 21, no. 4, p. 481, April 1993 and Chest, vol. 104, no. 6,p. 1711, December 1993.

With the present invention, a volume of approximately 2 cc is a suitablemaximum internal volume for the primary reservoir 66'; although, othervolumes may be used. A volume of 3 cc is a suitable combined internalfluid volume of the first and second conduits 204 and 212 for use (forexample) with conventional radial arterial catheters, although othervolumes may be used. Once the primary reservoir 66' is completely filledand the tether 84' is fully extended, further retraction on the handle34 will withdraw the cylinder divider piston 58' upward and away fromthe vented position. As discussed previously, when the cylinder dividerpiston 58' moves away from the vented position, the divider wipers 62contact the bore 22' tightly to provide a complete circumferential sealagainst the smooth bore 22' such that no further fluid can move from thedistal conduit 26' to the primary reservoir 66'. As the piston isfurther retracted (FIG. 9a), fluid moves into the secondary reservoir68'. The secondary reservoir 68' is then filled with a mixture of bloodand heparin solution with adequate volume to cause substantiallyundiluted blood to fill the first conduit 204 in response to thepressure gradient caused by the withdraw of fluid into the secondaryreservoir 68'. A volume of 3 cc of the primary reservoir 66' is asuitable volume; although, other volumes may be used. At this point, thevalve 214 can be closed so that no communication occurs between eitherthe patient and the distal conduit 18 of the syringe 5' or the patientand the high pressure source; and at this time, an aspirator, such as ablunt cannula having an indicator system to prevent pressure-inducedblood spurting, as discussed in my U.S. Pat. No. 5,114,400 (thedisclosure of which is hereby is incorporated by reference as ifcompletely disclosed herein) may be inserted into septum 211 to obtainan undiluted blood sample. Alternatively, measurements may be made by anex vivo system on the undiluted blood within the first conduit 204. Oncethe measurements have been made or the blood sample has been obtained,the nurse turns the valve 214 to its position opening fluidcommunication between the primary reservoir 66' and the patient and atthis time the nurse advances the piston handle 34'. As the piston 38'advances, hydraulic force within the primary reservoir 66' causes thecylinder divider piston 58' to advance, thereby causing the blood in thesecondary reservoir 68' to empty into the second conduit 212. After thedivider 58' has fully advance, any residual blood in the secondaryreservoir 68' is flushed out by the circumferential flow of flushsolution through slots 104' and out the flush flow space 116'. Thisclears the syringe 5' of substantially all blood. Any residual blood inconduits 204 and 212 and catheter 208 can be flushed back into the bloodvessel 209 using the flush valve 230 after the valve 214 is then againclosed to the syringe 5'. The process is now complete. This cycle may berepeated at any time an undiluted blood sample or ex vivo testing isdesired.

The invention can also be utilized for the sequential administration ofmedication and saline flush solution. The embodiment for medicationadministration can be identical to that utilized for single use bloodwithdrawal and which is incorporated as syringe 5 in thepreviously-described blood aspiration assembly. The method of use of thesyringe 5 for drug solution administration is shown in FIGS. 10-13. Inoperation for drug administration, the canula 111' is first insertedinto a vial 250 containing saline solution and the main piston 38 iswithdrawn by withdrawal of handle 34 until the primary reservoir 66 isfilled with saline. At this point, the nurse will feel a resistance tofurther withdrawal of the piston 38 which is induced by the detents 118engaging the wiper 60 transmitted through the now fully extended tether84. Also, a mark can be provided (as will be discussed with anotherembodiment) to indicate complete filling of the primary reservoir 66.The nurse then withdraws the cannula from the saline vial 250 andinserts the cannula 111 into the drug vial 260 (FIG. 12). The nurse thenwithdraws the handle 34 so that the cylinder divider piston 58 is pulledby the tether 84 past the detents 118 and the primary reservoir 66 fillswith drug solution (FIG. 13). Once the secondary reservoir 68 has beenfilled with adequate volume of drug solution, the nurse takes the filledsyringe 5 to the bedside and inserts the cannula 111' through the septumof a catheter or intravenous tubing system (not shown) in fluidcommunication with the patient. The nurse then advances the piston 38and the secondary reservoir 68 empties of drug solution into theintravenous tubing through hydraulic force within the primary reservoir66, as previously noted. When the injection of the fluid within thesecondary reservoir 68 is complete, the divider piston 58 has reachedthe venting position and engages the seats 109. At this point, furtheradvancement of the piston 38 causes the saline solution in the primaryreservoir 66 to flow through the slots 104 and through the flush flowspace 116 to flush around the lower face 59 of the divider piston 58 andout the distal conduit 18 and to flush the deadspace of the intravenoustubing and catheter with saline. The nurse withdraws the cannula whilecontinuing to apply pressure on the piston 38 during the flush maneuverto assure a positive pressure remains within the deadspace of the tubingof the catheter upon the withdraw of the cannula 111. The injection ofthe drug is now complete and the catheter and tubing system has beenflushed and residual positive pressure remains within the catheter andtubing system, thereby achieving a comprehensive sequential injection ofdrug and saline flush with only a single injection system and withoutthe need for multiple cannulas and multiples insertions. The syringe 5'may also be incorporated into conventional automatic mechanical orelectronic injection systems to allow automatic flushing after injectionwith a single syringe. The algorithms for these mechanical or electronicinjection systems can be adjusted to automatically accommodate the flushvolume of the primary reservoir so that the nurse need only identify theintended drug injection volume.

FIG. 14 illustrates another Blood Aspiration Assembly embodiment 200'with a fixed and preferably permanently attached syringe 5'. This designis intended for use with conventional multilumen catheters 390 or othercatheters having terminals 392 which may have low internal fluid volumes(often less than 1 cc) and which have been inserted into a blood vessel395' of a patient. The syringe 5' is attached to a main conduit 400having a proximal portion 410, the proximal portion 410 is intermediatea fluid injection site 420 and the syringe 5' and includes a bloodsampling site 430 and valve 434. The site 430 is reversibly connected tofluid source 435 which may be a syringe (not shown) or a bag of fluid,as shown. The conduit 400 further includes a distal priming fluidstorage portion 440 connected to the terminal 392. The distal portion440 is constructed to have a greater internal fluid volume than theproximal portion 410. The distal portion 440 functions to provideadequate priming of resident fluid storage distal the syringe 5' so thatthe primary reservoir 66' will have adequate resident fluid availablefor initial filling and for subsequent flushing of all blood from thesecondary reservoir 68' and the proximal portion 410 after the bloodspecimen has been obtained. The proximal portion 410 has a low internalfluid volume to allow complete flushing proximal the injection site 430with a minimal flush volume. The priming volume provided in the distalportion functions to add to the internal fluid volume of the catheter(which may be less than 0.5 cc) to allow adequate fluid for subsequentflushing. The priming volume can be, for example, 1-2 cc, but lesservolumes may be used with a smaller syringe 5'. The volume of the primaryreservoir 66' is predetermined to be less than the combined internalfluid volume of the catheter 390, its terminal 392, and the conduit 400(including the primary volume). In combination, volumes of 2 cc for thefirst conduit, 0.5 cc for the second conduit, and a primary reservoirvolume of 1.5 cc will provide an adequate flush volume to assure thatthe syringe and second conduit are adequately flushed with each bloodaspiration maneuver.

In operation, fluid from the fluid source 435 is disabled and the handle34 of the syringe is withdrawn. This causes the fluid stored in thedistal portion 440 to flow into the primary reservoir 66' (where it willbe used later to flush the syringe 5' and adjacent proximal portion410). Upon further retraction, blood enters the system 200' and fillsthe secondary reservoir 68'. The valve between the syringe 5' and thesampling site is then closed and a blood sample is obtained, as bycannula 111". The valve 424 is then opened and the handle 34' isadvanced, flushing the blood back into the patient, the fluid within theprimary reservoir 66' flushing the syringe 5' and proximal portion 410.Fluid flow can then be enabled through the injection site 430 to flushany residual blood in the distal portion 440 or catheter 390 back intothe blood vessel 395 of the patient.

Although the previously described preferred embodiment utilizingconfiguration of slots adjacent the distal end to providepositionally-enabled and disabled flow through the flow channel betweenthe primary and secondary reservoir has the advantage of minimizing thenumber of moving parts, this embodiment may require more complex moldingof the syringe barrel. Syringe barrels with smooth continuous boresthroughout are in wide clinical use and, for this reason, themanufacturing cost for such syringe barrels is extremely low. It would,therefore, be advantageous to provide an embodiment which does notrequire any modification of conventional smooth syringe barrels whichare presently in wide use and marketed, for example, by Sherwood MedicalCorporation and Becton Dickinson Corporation in many different sizes.Other corporations, likewise, produce such inexpensive syringe barrels.The utilization of conventional syringe barrels can substantially reducedevelopment time and, therefore, provide important value from acompetitive perspective and can result in more expeditious widespreadavailability so that the advantages disclosed herein can be more rapidlyrealized within healthcare delivery facilities.

The presently preferred embodiment for utilizing conventional syringebarrels is shown generally in FIGS. 15 and 16. The syringe 5" includesconventional syringe barrel 10" having a conventional main bore 22"which is preferably smooth and continuous in diameter throughout itslength. The main bore 22" extends to distal tapered portion 14" and thebore is in fluid connection with a distal conduit 22" extending todistal tip 18". The syringe 5" further includes a main piston 38"connected by a flexible tether 84" to divider piston 58". The dividerpiston 58" contains a tether valve 500. The valve 500 includes acylindrical plug 505 with upper surface 510. The plug 505 has a distalend 512 with an annular rim 514 for diverting flow, as will bedescribed. The plug 505 is connected to two radially-projecting legs 520having upper contact area 524 by flexure regions 530. The legs includeextensions or feet 540 having a radius 544, the feet 540 project axiallyaway from the legs 520. The plug 505 includes axial ribs 545 forproviding an annular flow area and to guide and retain the plug 505 andto provide pulling engagement against the divider piston 58" when thetether 84" is retracted, as will be described. The plug 505 is connectedto the tether 84", which is integral with the main piston retainer 82"for insertion and retention within the main piston 38". Generally, thestructure of the reservoir divider 58" is similar to that described withthe previously-discussed embodiment. However, the reservoir divider 58"with this embodiment includes a cylindrical central flow channel 550having a smaller proximal bore 560 connected to a larger main bore 570.The bore is further connected to two axially-projecting slots 574 forreceiving the legs 520. Four radial/circumferential slots or flowchannels 758 are further provided in fluid communication with the mainbore 570 for bi-directional flow and circumferential flush, as will bediscussed. The reservoir divider 58" includes fulcrum point 580 forcontacting leg contact area 524 and for inducing downward flexion of thelegs 520 through pivoting action about the radius 544 of feet 540 whenthe divider piston 58" is advanced downward and the feet 520 are pressedagainst the tapered portion 14".

In assembly, the tether valve 500 is inserted the reservoir divider 58"by first inserting the tether 84" through the bores in the tetherdivider 58" and seating the legs 520 within the slots 574. The reservoirdivider 58" is, with its associated tether valve 500, attached throughthe tether 84" to the main piston 58" is inserted into the bore 22 ofthe syringe 5 and advanced until the feet of the tether valve 500contact the distal tapered portion 14 of the syringe 5. At this point,further pressure upon the upperface 72" of the reservoir divider 58"causes the fulcrum point 580 to induce downward flexion of the legs 540around radius 544, thereby causing downward unseating deflection of thetether valve piston out of bore 560 and away from sealing contact withmain bore 570. This opens fluid communication between the primary andsecondary reservoirs 68 and 67.

Prior to operation, the main piston 38" is fully advanced, as describedabove, and the reservoir divider piston 58" is frictionally retainedadjacent the distal end 14" with the tether valve plug 505 displaceddownward from the seated position (as shown in FIG. 15). The syringe isoperated in a similar manner to that described for the previousembodiments and may be used in the same environments within the hospitaland in home patient care. Cannula 111" is initially placed in fluidconnection with a source of flush solution (not shown) and handle 34" isretracted which withdraws the main piston 38", enlarging the primaryreservoir 66. In response to the retraction of main piston 38", fluidenters the distal conduit 26" and passes through theradial/circumferential flow channels 758 through the central flowchannel 550 and into the secondary reservoir 68". During this time, thereservoir divider piston 58" is frictionally held. When the primaryreservoir 66" has been filled, the syringe 5" can then be connected to asecond fluid source (or in the case of blood aspiration, may already beconnected to a second fluid source, as previously described). The nursethen retracts the handle 34" further. This causes the tether 84" to urgethe plug 505 into the proximal bore 560 to occlude the proximal bore 560so that primary reservoir 66" is isolated from the distal conduit 26".Further retraction withdraws the cylinder divider piston 58" away fromthe fully advanced position to enlarge the secondary reservoir 68". Inresponse to enlargement of the secondary reservoir 68", fluid from thesecond fluid source enters the secondary reservoir 68". Once thesecondary reservoir 68" has filled, the syringe 5" contains fluid fromthe first fluid source within the primary reservoir 66" and fluid fromthe second fluid source within the secondary reservoir 68". As with theprevious embodiments, the nurse can then inject these fluids into thepatient in the reverse order in which they were obtained. To performthis injection, for example, the nurse inserts the cannula into an I.V.access port (not shown) and advances the handle 34", which pushes themain piston 38" downward, increasing pressure within the primaryreservoir 66". The hydraulic force within the primary reservoir 66"pushes the cylinder divider piston 58" downward since fluid cannotescape from the primary reservoir 66". Transmission of hydraulic forceto the plug 505 is limited by the limited upper surface area of the plug505, which can be reduced further than shown, so that the plug is notdisplaced from its seated position by the pressure within the primaryreservoir 66". Complementary detents (not shown) along the plug 505 andbore 570 can be provided if additional retention security is desired. Asthe cylinder divider piston 58" advances, the fluid is injected into thepatient from the secondary reservoir 68". When the secondary reservoir68" is nearly empty, the feet 540 of the tether valve 500 contacts thetapered distal end 14" of the barrel 22", causing downward displacementof the plug 505 from the proximal valve bore 560, as previouslydescribed. This allows fluid to escape through the proximal bore 560from the primary reservoir 66" into the secondary reservoir 68" tocompletely flush the secondary reservoir 68" and distal conduit 26". Toprovide a comprehensive flush of the flow space 116", flow is channeledthrough the main valve bore 570 which is occluded at its distal end bythe annular rim 514 of the plug 505 to force the flow through theradial/circumferential slots 758 into the flow space 116", therebycreating a turbulent circumferential flushing action.

FIG. 23 shows the sequential syringe 5''' incorporated into an automaticsyringe pump 600. The syringe is in fluid connection with a conduit 602for insertion into a blood vessel. The syringe handle 34''' is engaged,with handle holder 604 connected to pumping mechanism 606 for advancingthe syringe handle 34''', as is known in the art. The syringe caninclude a mechanical or electronic volume-selector for selecting thespecific drug solution volume and a selector for selecting a specificflush solution volume. Syringe pump 600 can include an algorithm forautomatically adjusting for the flush volume contained within primaryreservoir 66''' so that the nurse need not be concerned with selectingthe specific flush volume within primary reservoir 66'''. This isadvantageous in reducing the work and concern of the nurse related tothe flush volume. Syringes having specific volumes and incorporated intothe syringe pump can include automatic adjustments for preset flushvolumes related to the specific size of the syringe.

Many modifications can be made within the scope of this teaching. Forexample, with intermittent blood sampling, the force to overcome thedetent 118 can be adjusted by the angle and height of the detent so thatthe vacuum from a conventional evacuated container will not overcome thedetent 118 to positively prevent the resident fluid within the primaryreservoir from being transferred. Other means for so restraining thefurther advancement of the cylinder divider piston 58 in response toinsertion of the cannula into an evacuated container after the primaryreservoir 66 has emptied can be provided. For example, detents (notshown) could be provided along the handle 34 to engage a complimentarydetent (not shown) at the syringe barrel base to achieve suchpositionally activated restraint of further forward advancement of thehandle. The vent portion can include other means for providing variancein shape or dimension between the wipers along the divider and the boreso that the tight seal is broken at the venting portion to form a flowchannel between the reservoirs, or by otherwise providing a regionadjacent the distal end wherein the bore shape changes in relationshipto the divider so as to cause the divider to become free fromtight-sealing contact with the bore. In such embodiments, it ispreferable that the divider, when in the sealing contact with the bore.In such embodiments, it is preferable that the divider, when in theventing position, becomes free from tight-sealing contact in a nearlycomplete circumferential manner so that fluid may flow about the entireperimeter of the divider to completely flush any deadspace within theprimary chamber and distal conduit free of residual blood or drugsolution with a minimal amount of fluid. This is most important when thesyringe is being used as part of a blood aspiration assembly forrepetitive blood isolation since it is desirable to prevent blood fromaccumulating within the deadspace of the syringe. To achieve reductionin cost in molding the barrel of the syringe and to avoid providing thevalve on the divider piston, the vent portion can be provided as atapered circumferential expansion or undercut of the diameter of thebore adjacent the distal end and the wipers could be constructed todeflect when not tightly pressed against the bore within the expandedventing portion to allow fluid to escape around the wipers. A limitedundercut may be achieved without the need for a collapsible core and,therefore, may substantially reduce the cost of molding. Such undercutscould also be used to provide the stops and seats of the syringe.

Other means for retracting the divider piston from the venting positioncan be provided. For example, the divider piston may be connected to themain piston by a flexible transparent chamber which can collapse whenthe main piston is advanced toward the divider piston when the flowchannel is open. Furthermore, other means for providing apositionally-enabled and/or disabled fluid flow through a flow channeland valve mechanism may be provided including, for example, flap valveswhich allow flow into the primary reservoir, but which are closed bypositive pressure in the primary reservoir. Such valves may be, forexample, deflected open by pins when the pins contact the distal taperedend to allow the positive pressure to be released by expelling fluidpast the deflected flaps. Other means for mechanically linking the mainpiston and divider piston will become evident to those skilled in theart and are included within the scope of this teaching. For example,although, as noted previously, a flexible tether is preferred, thelinking or tensile element between the main piston and the dividerpiston can be either rigid or flexible. The linking element preferablydirectly connects the pistons through the element, but does not inhibitadvancement of the main piston toward the divider piston when the flowchannel is open and further allows independent retraction of the mainpiston with respect to the divider piston when the primary reservoir isincompletely filled. The linking element also preferably provides formechanical combined mutually equivalent retraction of the main pistonand the divider piston during retraction of the main piston after theprimary reservoir has been filed. A rigid element which is connecteddistally to the divider piston and which telescopes through a bore inthe main piston and which includes a proximal stop at a preset distanceproximal to the main piston could provide a similar function to thepreferred flexible linking element by allowing the rigid element totelescope through the main piston when the main piston is advanced, butcausing retraction of the divider piston through retraction on the rigidlinking element after the main piston is retracted such that it engagesthe proximal stop of the rigid element.

Although the presently preferred embodiments of this invention have beendescribed, it will be obvious to those skilled in the art that variouschanges and modifications may be made therein without departing from theinvention. Therefore, the claims are intended to include all suchchanges and modifications which may be made therein without departingfrom the invention. Therefore, the claims are intended to include allsuch changes and modifications that fall within the true spirit andscope of the invention.

We claim:
 1. A system for the sequential and repetitive aspiration andinjection of a first liquid and blood, the system comprising:a. asyringe having a variable volume chamber having a distal end and anopening in said end, and further having an internal displacement volumeand piston to vary said internal displacement volume; b. a chamberdivider for separating said internal volume into at least first proximaland second distal variable volume reservoirs, said chamber divider beingmoveable along said chamber, said chamber divider being positionedadjacent said end prior to withdrawal of said first liquid into saidsyringe, said first proximal reservoir having a maximum displacementvolume for receiving said first liquid; c. a flow channel along saidsyringe, said flow channel being capable of providing flow connectionbetween the proximal reservoir and the distal reservoir; d. a valvecapable of at least one disabling and enabling flow between saidproximal reservoir and said distal reservoir through said flow channel;e. a tensile element for linking said piston and said chamber divider sothat when said piston is moved away from said chamber divider, and saidproximal reservoir is at least partially filled with said first liquid,said chamber divider is urged by said tensile element away from saiddistal end of said chamber to enlarge said distal reservoir and towithdraw said blood into said distal reservoir; f. a conduit having adistal terminal, said conduit being in fluid connection with saidchamber and in communication with the blood vessel of a patient andcontaining said first liquid intermediate said chamber and said distalterminal; g. said flow channel and said conduit being sized andconfigured such that after said maximum volume of first liquid has beenwithdrawn into said proximal reservoir and said blood has been withdrawninto said distal reservoir, said maximum volume of first liquid issubstantially free from blood, and subsequent displacement of saidmaximum volume of first liquid back through said valve is sufficient todisplace all said blood from the syringe when said piston is advancedalong said chamber so that upon repetitive withdrawal and advancement ofsaid piston, blood is not retained within said syringe.
 2. The syringeof claim 1 wherein said chamber divider is a second piston and whereinsaid valve comprises said chamber divider for disabling flow betweensaid proximal reservoir and said distal reservoir.
 3. The syringe ofclaim 1 wherein said tensile element having a maximum extended length,said length defining the maximum displacement volume within saidproximal reservoir.
 4. A system for sequentially and repetitivelyaspirating a first solution into a primary reservoir and a secondsolution comprising blood into a secondary reservoir, the systemcomprising:a. a syringe having a cylindrical barrel defining a borehaving a distal end, said distal end having an opening through saiddistal end, said bore being in fluid connection with said opening; b. apiston sized to be received tightly within said bore and to seal aboutsaid bore intermediate said piston and said distal end, said pistonhaving a handle for movement of said piston along said bore to define avariable volume chamber within said bore, said piston further comprisinga proximal portion and a distal portion, said proximal portion beingconnected to said distal portion by an element between said proximalportion and said distal portion, said element being retractable byretraction of said proximal portion to an extended position whereinretraction force is exerted through said element upon said distalportion, said proximal portion being moveable away from said distalportion to define a primary variable volume reservoir intermediate saidportions and to draw said first solution into said primary reservoir,said primary reservoir having a maximum volume, said distal portionbeing movable along said bore and away from said distal end when saidhandle is retracted and when said element is extended to define saidsecondary variable volume reservoir intermediate said distal portion andsaid distal end, said first solution being trapped within said primaryreservoir by said proximal and said distal portions when said element isretracted to said extended position, said distal portion being moveabletoward said distal end when said primary reservoir is filled with saidfirst solution, said first solution exerting hydraulic force againstsaid distal portion to urge said distal portion toward said distal endwhen said proximal portion is moved against said primary reservoir; c. aflow channel for providing flow communication between said primaryreservoir and said secondary reservoir, said trapped first solutionescaping from said primary reservoir through said flow channel when saiddistal portion has been advanced to a position adjacent said distal endand when said proximal portion is further advanced toward said distalportion, said first solution within said primary reservoir functioningto flush said secondary reservoir free of blood; d. a conduit having adistal terminal, said conduit being in fluid connection with saidchamber and in communication with the blood vessel or a patient andcontaining said first solution intermediate said chamber and said distalterminal; e. said flow channel and said conduit being sized andconfigured such that after said maximum volume of first solution hasbeen withdrawn into said proximal reservoir and said blood has beenwithdrawn into said distal reservoir, said maximum volume of firstsolution is substantially free from blood, and subsequent displacementof said maximum volume of first solution back through said valve issufficient to displace all said blood from the syringe when said pistonis advanced along said barrel so that upon repetitive withdrawal andadvancement of said piston, blood is not retained within said syringe.5. A system for isolating a volume of undiluted blood within a conduit,system comprisinga. a conduit having a blood testing portion and furtherhaving a distal end for fluid connection with a blood vessel, saidconduit having an internal volume filled with flush solution; b. amulti-compartment syringe including a proximal reservoir and a distalreservoir, said proximal reservoir having a target volume, said syringebeing connected to said conduit, said conduit defining a first internalvolume intermediate said syringe and said distal end; c. said firstinternal volume of said conduit being sufficient to prevent blood fromflowing from said blood vessel into said proximal reservoir when saidtarget volume of flush solution is displaced into said proximalreservoir from said conduit; d. said conduit defining a second volumeintermediate said sampling port and said blood vessel, and wherein saidtarget volume of said proximal reservoir is greater than said secondvolume; e. said distal reservoir having a variable volume and defining astorage volume for mixed blood and flush solutions and wherein the sumof said target volume of said proximal reservoir and said storage volumeof said distal reservoir is sufficiently greater than said second volumeof said conduit such that upon withdrawal of said sum into said syringeand the displacement of blood into said conduit in response to saidwithdrawal, said second volume of flush solution is substantiallydisplaced from intermediate said sampling port and said blood vessel byundiluted blood from said blood vessel.
 6. The system of claim 5 furtherincluding a fluid source in flow connection with said conduit, saidfluid source having an elevated fluid pressure relative to said conduit.7. The system of claim 6 further including a 3 way valve positionedintermediate said conduit, said syringe, and said fluid source forselective fluid connection between at least said fluid source and saidconduit and further between said syringe and said conduit.
 8. The systemof claim 6 further including a pressure transducer mounted adjacent saidconduit for monitoring pressure within said conduit.
 9. The system ofclaim 6 further including an ex vivo blood testing monitor mountedadjacent said blood testing portion of said conduit.
 10. A system forautomatically separating flush solution from blood within a syringe, thesystem comprising:a. a conduit having a blood testing portion andfurther having a distal end for fluid connection with a blood vessel,said conduit having an internal volume filled with flush solution; b. amulti-compartment syringe including a proximal reservoir for storingflush solution, said proximal reservoir having a target volume, saidsyringe being connected to said conduit, said conduit defining a firstinternal volume intermediate said syringe and said distal end; c. saiddistal reservoir having a minimum volume, the sum of said first internalvolume of said conduit and said minimum volume of said distal reservoirbeing sufficiently greater than said target volume of said proximalreservoir, so that upon displacement of said target volume of flushsolution into said proximal reservoir from said conduit, blood from saidblood vessel flows into said conduit and said distal reservoir but blooddoes not flow into said proximal reservoir so that upon saiddisplacement, flush solution can be automatically separated from bloodwithin said syringe.
 11. The system of claim 10 wherein said distalreservoir has a variable volume and defines a storage volume for storingmixed blood and flush solution, said target volume and said storagevolume into said syringe from said conduit, sufficient blood from saidblood vessel flows into said conduit in response to said withdrawal todisplace substantially all flush solution from said blood testingportion.
 12. The system of claim 11 wherein said target volume comprisesthe maximum displacement volume of said proximal reservoir.
 13. In ablood isolation system for use with a catheter having a set internalvolume, the system functioning for isolation of a volume of undilutedblood within a conduit, the system further including a conduit having asampling port and further having a distal end for fluid connection witha blood vessel through a catheter, said conduit having an internal lumenfilled with flush solution, said conduit further defining a firstinternal conduit volume intermediate said sampling port and said bloodvessel, improvements comprising:a. a multi-compartment syringe includinga proximal reservoir and a distal reservoir, said proximal reservoirhaving a target volume, said syringe being in fluid connection with saidconduit and mounted with said conduit; b. said distal reservoir having avariable volume and defining a storage volume for storage of mixed bloodand flush solution; c. the sum of said target volume of said proximalreservoir and said storage volume of said distal reservoir beingsufficiently greater than said first internal volume of said conduit andsaid set volume of said catheter such that upon withdrawal of said suminto said syringe and the displacement of blood into said conduit inresponse to said withdrawal, said first volume of flush solution issubstantially displaced from intermediate said sampling port and saidblood vessel by undiluted blood from said blood vessel.
 14. The systemof claim 13 wherein said target volume is the maximum displacementvolume of proximal reservoir.
 15. A method for repetitively accessingundiluted blood, said method including steps of:a. disposing a conduitcontaining liquid in fluid connection with a blood vessel; b. connectinga multi-compartment syringe into fluid connection with said conduit,said syringe having a proximal reservoir and a distal reservoir; c.withdrawing flood free liquid from said conduit into said proximalreservoir and storing said blood free liquid within said proximalreservoir; d. withdrawing a volume of a mixture of blood and liquid intosaid distal reservoir, the volume of said mixture being sufficient todraw on diluted blood onto said conduit; e. accessing said undilutedblood; f. returning said mixture of blood and liquid from said distalreservoir into said conduit; g. flushing said distal reservoir free ofblood by flowing said blood free liquid from said proximal reservoirinto said distal reservoir.
 16. The method of claim 15 further includingthe steps of:a. disposing a high pressure fluid source in fluidconnection with said conduit; b. after the step of flushing said distalreservoir, further activating flow from said high pressure fluid sourceinto said conduit flush said conduit free of blood.
 17. A method forrepetitively accessing undiluted blood, said method including stepsof:a. disposing a conduit containing liquid in fluid connection with ablood vessel; b. connecting a multi-compartment syringe into fluidconnection with said conduit, said syringe having a proximal reservoirand a distal reservoir; c. displacing blood into said conduit bywithdrawing liquid from said conduit into said proximal reservoir; d.discontinuing said withdrawing of said liquid before substantially anyblood enters said proximal reservoir and storing said liquid within saidproximal reservoir; e. withdrawing a volume of a mixture of blood andliquid into said distal reservoir, the volume of said mixture beingsufficient to draw undiluted blood into said conduit; f. accessing saidundiluted blood; g. returning said mixture of blood and liquid from saiddistal reservoir into said conduit; h. flushing said distal reservoirfree of blood by flowing said liquid from said proximal reservoir intosaid distal reservoir.
 18. A method of sampling undiluted blood into ablood collector from a blood sampling port of a conduit in fluidconnection with a blood vessel, said conduit being filled with flushsolution, said method comprising:a. a disposing syringe in fluidconnection with said conduit, said syringe having a proximal reservoirand a distal reservoir; b. withdrawing said flush solution from saidconduit into said proximal reservoir, discontinuing said withdrawal offlush solution into said proximal reservoir before blood enters saidproximal reservoir; c. withdrawing a mixture of blood and flush solutioninto said distal reservoir until diluted blood is displaced into saidconduit adjacent said sampling port; d. flowing undiluted blood fromsaid sampling port into said blood collector.